The researchers improved their acoustic tweezers, making them lift particles while achieving stability. (Image Credit: Tokyo Metropolitan University/YouTube)
Sound waves are capable of exerting a physical force, especially when someone stands beside a loudspeaker. Arranging speakers at the correct frequency, amplitude, and phase can lead to sound wave superimposition, setting up a pressure field to push, lift, and hold objects. Tokyo Metropolitan University researchers recently improved their acoustic tweezers, enabling them to pick up particles via sound waves. Previously, this device already lifted objects on reflective surfaces, but it experienced stability issues at the time. By applying an adaptive algorithm to boost controllability, the tweezers can now achieve greater stability while lifting those particles. Miniaturizing the technology could lead to it being used in varying environments, such as space.
In 2021, the team developed a hemispherical array of small ultrasound transducers that can lift and move millimeter-sized particles without physical contact. These transducers relied on a special algorithm to set up sound pressure fields that lifted and moved objects. Even then, the tweezers still had stability issues.
So the team figured out how to improve the setup’s ability to achieve particle lift on rigid surfaces. The transducers have two control modes, where the opposing halves of the hemispherical array drive in and out of phase. In this case, different modes perform specific tasks. An in-phase excitation mode makes it easier to lift and move a particle close to the surface, and it can target particles from one centimeter apart. The out-of-phase mode is responsible for placing the lifted particle in the middle of the array. With adaptive switching between each mode, the team can take advantage of both modes to perform a stable, well-controlled lift while providing enhanced stability in the trap.
This technology could eventually lead to sample manipulation that needs to be contamination free. In addition, the team hopes it can be used in space, where gravity won’t interfere.
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